With the user's higher and higher requirements for wireless access rate, WLAN which can provide high-rate data access in a small area is being developed. WLAN includes various different techniques, and at present a widely applied technical standard is IEEE 802.11b, which adopts 2.4 GHz frequency channel and can reach a highest data transmission rate as 11 Mbps. IEEE 802.11g and Bluetooth technique also use this frequency channel, and IEEE 802.11g can reach the highest data transmission rate as 54 Mbps. Other new techniques, such as IEEE 802.11a and ETSI BRAN Hiperlan2, utilize the frequency channel of 5 GHz, and the highest data transmission rate can also be 54 Mbps.
Although there are various different wireless access techniques, most of WLANs are used to transmit Internet Protocol (IP) data packets. In a wireless IP network, the adopted specific WLAN access technique is generally transparent to the upper IP. In the WLAN access technique, WLAN user terminal's wireless access is implemented. by using an Access Point (AP), and an IP transmission network is established by means of network control and connection of connection equipments.
With the popularization and development of WLAN techniques, intercommunication between WLAN and various wireless mobile communication networks, such as Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA) system, Wideband CDMA (WCDMA) system, Time Division-Synchronous CDMA (TD-SCDMA) system or CDMA2000 system, is becoming the focus of current research. In the 3rd Generation Partner Project (3GPP) Organization for Standardization, it is prescribed that a WLAN user terminal can be connected to the Internet or Intranet via a WLAN access network, and can also be connected to a home network of 3GPP system or a visited network of 3GPP system via a WLAN access network. Specifically speaking, a WLAN user terminal is connected to a 3GPP home network via a WLAN access network in the case of local access, as shown in FIG. 2; when the WLAN user terminal is roaming, as shown in FIG. 1, a WLAN user terminal is connected to a 3GPP visited network via a WLAN access network, and part of the entities in the 3GPP visited network are respectively connected to corresponding entities in the 3GPP home network. For example, a 3GPP Authentication Authorization Accounting (AAA) agent in the 3GPP visited network is connected to a 3GPP AAA server in the 3GPP home network, a WLAN Access Gateway (WAG) in the 3GPP visited network is connected to a Packet Data Gateway (PDG) in the 3GPP home network, etc. Here, FIG. 1 and FIG. 2 are schematic diagrams illustrating the framework for intercommunication between a WLAN system and a 3GPP system in case of roaming and non-roaming respectively.
With reference to FIGS. 1 and 2, it can be seen a 3GPP system mainly includes a Home Subscriber Server (HSS)/Home Location Register (HLR), a 3GPP AAA server, a 3GPP AAA agent, a WAG, a PDG, a Charging Gateway (CGw)/Charging Collection Function (CCF) and an Online Charging System (OCS). WLAN user terminals, all entities of a WLAN access network and a 3GPP system jointly constitute a 3GPP-WLAN interaction network, which can be-taken as a WLAN service system. Here, the 3GPP AAA server is responsible for implementing authentication, authorization and accounting for users, collecting and transferring charging information from the WLAN access network to the charging system. The PDG takes charge of transmitting user data from the WLAN access network to the 3GPP network or other packet networks. The charging system is mainly in charge of receiving and recording user charging information from the network. The OCS is in charge of instructing the network to periodically transmit online charging information according to charging situation of online charged users, as well as in charge of statistics and control.
In case of non-roaming, when a WLAN user terminal expects to be directly accessed to Internet/Intranet, the WLAN user terminal can be accessed to Internet/Intranet via a WLAN access network after finishing access authentication and authorization with an AAA server (AS) via the WLAN access network. If the WLAN user terminal also expects to access 3GPP Packet Switch (PS) domain service, it can further apply to 3GPP home network for Scenario3 service, namely, the WLAN user terminal requests AS of 3GPP home network for Scenario3 service authorization, the AS of 3GPP home network performs service authentication and authorization upon this service authorization request, if successful, the AS will send an access allowance message to the WLAN user terminal and allocate corresponding PDG for the WLAN user terminal, thereby the WLAN user terminal can access 3GPP PS domain service after the channel between the WLAN user terminal and the allocated PDG is established. Meanwhile, the CGw/CCF and the OCS record charging information according to network utilization situation of the WLAN user terminal. In case of roaming, when a WLAN user terminal expects to be directly accessed to Internet/Intranet, the WLAN user terminal can apply to 3GPP home network for accessing the Internet/Intranet via a 3GPP visited network. If the WLAN user terminal also expects to further apply for Scenario3 service and access 3GPP Packet Switch (PS) domain service, the WLAN user terminal needs to initiate a service authorization procedure towards the 3GPP home network through the 3GPP visited network. The procedure is also performed between the WLAN user terminal and the AS of 3GPP home network. If the authorization is successful, the AS will allocate corresponding home PDG for the WLAN user terminal, thereby the WLAN user terminal can access 3GPP PS domain service after the channel between the WLAN user terminal and the allocated PDG is established.
As shown in FIG. 3, in a 3GPP-WLAN intercommunication network, if a WLAN is connected to multiple 3GPP visited networks which mean Visited Public Land Mobile Networks (VPLMNs), namely multiple mobile communication operation networks, at the same time, the WLAN user terminal will select a desirable VPLMN network after being accessed to this WLAN. For example, in China, a WLAN access network is connected to both VPLMN operation networks of China Mobile and China Unicom at the same time, then, a user of China Unicom needs to instruct WLAN access network to access VPLMN operation network of China Unicom when accessed to WLAN.
Taking another example, a French user roams to a certain WLAN in China, if this French user's home network has roaming protocols with both China Mobile and China Unicom, in case of the WLAN access network being connected to both China Mobile and China Unicom, this French user needs to select a VPLMN network to access after being accessed to the WLAN. Regarding how a WLAN user terminal selects a desirable access network and notifies WLAN access network of the information of the network selected by itself, as well as how the 3GPP-WLAN intercommunication network performs the interaction according to information of the network information selected by the WLAN user terminal, a resolving scheme has been put forward in another patent application whose basic idea is that a WLAN user terminal transmits network selection information to a WLAN access network by means of an access authentication request, the WLAN access network identifies the desirable mobile communication operation network to be accessed by the WLAN user terminal according to the carried network selection information and connects the current WLAN user terminal to the selected network for access authentication and subsequent operations.
However, it will consume a great amount of network resources if a WLAN user terminal selects a network every time. For instance, under the condition that a user is roaming in another place and the user's home mobile communication operation network is not directly connected to the WLAN access network in which the user is currently located, if the WLAN user terminal notifies the WLAN access work of the user's home network as initially selected network every time, every access will trigger the network selection procedure, thereby the WLAN network sends network selection information to this WLAN user terminal and this WLAN user terminal will access this selected network after judging and selecting, leading to network consumption and delay of user's access. However, if the last selected mobile communication operation network is simply adopted, as for a WLAN user terminal that has entered a new WLAN network, it may not be guaranteed that current selected network is the optimal PLMN network of this WLAN user terminal. In other words, when a WLAN user terminal is located in a new WLAN network, although the default mobile communication operation network to access or the previously selected mobile communication operation network has roaming relation with the visited network of this WLAN user terminal and may be available, this new WLAN network in which this WLAN user terminal is currently located may be directly connected to a Home Public Land Mobile Network (HPLMN) or other better VPLMNs. In such a case, since there is already default or selected mobile communication operation network for routing, new network selection is not allowed, therefore, it is not guaranteed that the WLAN user terminal can select the optimal PLMN network for the current WLAN network, such as a HPLMN. So far no one has put forward a specific resolving scheme in terms of the problem as, when a WLAN user terminal is located in a new WLAN, how to guarantee the WLAN user terminal to select a proper optimal mobile communication operation network at any time if a WLAN is connected to multiple mobile networks.